#include <iostream>

using namespace std;

int sum(int l, int r) {
    int s = 0;
    for (int i = l; i <= r; i++) {
        s += i;
    }
    return s;
}

int main() {
    int l, r;
    cin >> l >> r;
    cout << sum(l, r) << endl;

    return 0;
}
